Hypodermic needles are used on a regular basis by medical professionals such as doctors, nurses and other medicine related fields. The typical hypodermic needle has a syringe body with a hollow interior cavity. A piston is slideably disposed within the syringe body and may be traversed between a proximal position and a distal position. A shaft may be fixedly attached to the piston and extend through a proximal portion of the syringe body. A thumb platform may be attached to the proximal portion of the shaft. The thumb platform may be traversed toward or away from the proximal portion of the syringe body to traverse the piston toward the distal position or the proximal position, respectively. The distal portion of the syringe body may have a needle attached thereto. The syringe body piston and the distal portion of the syringe body define a variable fluid chamber. The variable fluid chamber may be filled with fluidic medication to be injected into a patient. In the typical hypodermic needle, the needle is  fixedly engaged to the distal portion of the syringe body. Also, the piston may be positioned anywhere between the proximal position and the distal position. The user may release the thumb platform and the piston will remain at such position because there is no biasing force urging the piston back toward the retracted position.
In use, the hypodermic needle may be provided to the medical professional without fluidic medication filled within the variable fluid chamber. The user may traverse the piston toward the distal position. The needle of the hypodermic needle may be inserted into a fluidic medication container. The user may retract the piston toward the proximal position thereby transferring fluidic medication from the container into the variable fluid chamber. The user may release the thumb platform and the piston is not traversed to the proximal position because there is no biasing force which urges the piston back toward the proximal position.
The medical professional may remove trapped air within the variable fluid chamber by inverting the syringe such that the needle is pointing upwardly, tapping the outside of the syringe body to urge the air bubbles toward the needle, and depressing the thumb platform slightly to eject the air bubbles from the variable fluid chamber. The medical professional may release the thumb platform, and the piston is not retracted back toward the proximal position. The medical professional may insert the needle into a skin of the patient and inject the fluidic medication into the patient by traversing the piston toward the distal position. Once the piston is at the distal position, the fluidic medication is injected into the patient and the medical professional removes the needle from the patient. At this point, the needle contaminated and exposed and is a health-risk to the medical professional or other people who may handle the syringe. Also, drug addicts may reuse the needle.
The risks associated with the spread of blood-borne pathogens through use of prior art hypodermic needles are significant and well documented. In recent years, the public has become increasingly aware of the health hazards associated with needle reuse and accidental needle prickings. These risks are most prevalent among certain groups of people, such as drug addicts, drug users (e.g., diabetics), medical personnel and healthcare providers. In fact, more than twenty blood-borne pathogens can be transmitted by the reuse of needles or accidental needle prickings, just a few of which include human immunodeficiency virus (HIV), acquired immunodeficiency syndrome (AIDS), hepatitis B, hepatitis C, syphilis, malaria, tuberculosis, and herpes. 
In 1997, the Centers for Disease Control and Prevention (CDC) sponsored a study which found that approximately 76% of needle pricking injuries could be avoided by using safety needles. As a result, needle legislation has now been introduced in approximately twenty-five states and in the District of Columbia. In fact, such safety needle legislation has already been signed into law in a number of states including California, Texas, Tennessee, New Jersey and Maryland. In addition, the Occupational Safety and Health Administration (OSHA) has promulgated a Blood-borne Pathogens Standard requiring employers to evaluate the effectiveness of existing controls designed to minimize or eliminate employee occupational exposure and to review the feasibility of instituting more advanced controls. Furthermore, the Food and Drug Administration (FDA), in an effort to protect health care workers, has set forth guidelines suggesting specific features that a safety syringe should possess. These include a safety feature that is not only simple and self evident to operate, thus requiring little or no additional training to use effectively, but also a safety feature that is an integral part of the apparatus. In other words, the guidelines suggest that the safety feature itself be unremovable and utilization of the safety feature be unavoidable. (www.osha-slc.gov/SLTC/needle stick/saferneedledevices/saferneedledevices.html; www.seiu.org).
As a result of the foregoing state legislation and agency guidelines, a great amount of time, effort and money has been invested by syringe manufacturers in developing syringes with safety needle designs. Presently, there are at least 250 types of safety syringes. However, the safety syringes that currently exist have been criticized for generally being too expensive to manufacture and having a safety feature that is not an integral part of the safety syringe. Another criticism includes safety syringes that are not economically feasible because operation of the safety feature is not self evident and therefore additional training is required to use the apparatus effectively. Additionally, the safety feature of at least one safety syringe is simply ineffective at preventing the transmission of blood-borne pathogens due to “reflux” blood contamination.
Of the current safety syringes, safety syringes using a spring mechanism are the most common for automatically retracting a hollow needle after injecting a fluid. However, these safety syringes are typically more expensive because of the required incorporation of additional materials for manufacture. Standard or conventional hypodermic needle syringes typically cost from five to seven cents each. On the other hand, the median increase in cost for a safety syringe is approximately thirty cents or more. At first glance, this minimal cost increase does not seem  significant. However, after considering the thousands, if not millions, of needles used each year, the resultant increase in annual cost for utilizing the more expensive safety syringe is unfortunately excessive.
Another syringe has been created that avoids some of the additional cost associated with spring mechanism safety syringes. This syringe, found in U.S. Pat. No. 6,413,236, entitled “Automatically Retractable Needle Safety Syringe,” issued on Jul. 2, 2002, seeks to solve the problem of needle reuse and accidental needle prickings through use of a vacuum. As disclosed therein, the safety syringe is configured to automatically retract the needle portion of the syringe into the body of the syringe utilizing a vacuum within the syringe, such that after a single use, the syringe may not be reusable nor lead to an accidental pricking.
As understood, the syringe of U.S. Pat. No. 6,413,236 utilizes vacuum pressure to exert an automatic retracting force upon the needle. Apparently, the syringe includes a plunger and a needle holder (to which the needle is attached) and is configured to frictionally engage the plunger with the needle holder. Once engaged with the needle holder, the vacuum pressure inside the syringe exerts the retracting force upon the plunger, which causes the plunger to remove the needle holder/needle and pull it into the syringe itself. After being completely retracted, the needle does not protrude out of the syringe body and the syringe cannot be reused nor accidentally prick an individual.
The aforementioned retractable safety syringes have helped alleviate many of the problems associated with accidental needle prickings and reuse of hypodermic needles. However, due to the configuration and retraction force inherent in the vacuum or spring mechanism aspect of these syringes and others like them, the user of the syringe may often experience difficulties in its use. Specifically, due to the vacuum pressure or spring mechanism, which exerts an automatic retracting force upon the plunger, the plunger may automatically retract at an undesirable time.
It is an apparent object of these syringes to retract the plunger when the needle holder has been frictionally engaged with the plunger. However, automatic retraction of the plunger prior to frictional engagement with the needle holder may often be very problematic. For example, automatic retraction may make syringe handling very difficult between the time the fluid is drawn to the time the fluid is emptied. In effect, a user must manually maintain the position of the plunger by exerting a force to counter the automatic retracting force. Otherwise,  the plunger will retract. Retraction of the plunger may be a nuisance if the syringe has not been introduced into the subject. However, while the needle is introduced into the subject, retraction of the plunger could effectively result in drawing fluid therefrom instead of the intended injection of fluid into the subject. This situation could be very harmful and lead to various unfortunate consequences.
Therefore, a need exists for an effective and efficient, inexpensive safety syringe that is simple and self evident to operate and integrally comprises a safety feature having a hollow needle that protectively retracts automatically after a single injection, but that mitigates against automatic retraction of the needle prior to completion of use. Further, there is a need in the art for an automatically retractable safety syringe that mitigates against automatic retraction of the needle during administration of the fluid injected therewith.